This invention relates to an addressable cable television control system. More particularly, the present invention relates to a cable television system having a multiple-function addressable converter and including data transmission in video format during the vertical interval of the video field or during substantially the entire video field.
In recent years, the availability of cable television programs and services for the general public has expanded rapidly. Communication satellites have enabled nationwide programming for a number of "super stations". Sophisticated two-way interactive cable communication systems have laid the groundwork for a wide spectrum of cable television and data communication services for the consuming public. After years of development, cable television systems have been or are now being installed in many major cities to provide the television consumer with a vast array of programming choices as well as many other services which can be utilized at home, such as shopping, banking and schooling. Other services provided by such systems include home security monitoring, medical and emergency alert signaling and information retrieval.
In order to provide these new services and programs in a systematic and efficient manner, generalized control systems are required which can supervise access to both one-way and two-way sophisticated cable communication systems having different degrees of complexity. Control is required to differentiate and limit access on several bases, including different levels or tiers of subscribers to different television channels, and different programs and events on a given channel. In addition, for many subscribers it is desirable to be able to limit access to certain programs because of the program subject matter. Presently, there are no cable systems having this degree of sophistication in controlling program access. Even simpler conventional cable systems which provide for limiting program access must be two-way interactive systems requiring more complex and expensive equipment than one-way systems.
Besides this problem of coordinating cable communications, the need for efficiency in the transmission of data has become increasingly apparent. Although approximately 55 video and sound channels are presently available between the allocated television frequencies of 50 and 400 megahertz, the varied types of possible cable television programming and data transmission services require the efficient utilization of these frequencies. For example, cable television programming includes movies, special events, news, consumer programming, community access and religious programming. An almost limitless range of data can be provided, including reports on stock and money markets, weather reports, airline schedules, shopping directories, entertainment schedules, traffic reports, home security data emergency and first aid information and unlimited library textual information. The possibility for cable system operators to lease available cable channels to private concerns for these and other services makes it imperative that cable transmission control be efficient and flexible. In order to effectively utilize the available portion of the electromagnetic spectrum for such a wide variety of programming and data transmission, the cable system should be able to process the data quickly and efficiently while using relatively simple and inexpensive equipment which is affordable to the general consuming public.
In the last few years, various experiments have been conducted regarding the transmission of data over the vertical blanking interval of a normal television signal. This interval in the video signal occurs 60 times each second as the cathode ray tube beam sweeps from the buttom to the top of the TV screen and is relatively unused for the transmission of data. Some early systems such as that shown in U.S. Pat. No. 3,769,579 issued Oct. 30, 1973, utilized the vertical interval for transmitting control signals to individual transponders at the subscriber locations. More recently, there has been experimentation with television broadcasting systems which transmit visual data on the vertical blanking interval, referred to as teletext transmission, for display as pages of text on suitably equipped television receivers. These experimental systems have generally been limited to over-the-air broadcasting of teletext transmissions for a single channel, and the necessary apparatus for cable television systems has been regarded as too complicated and expensive to be practical when compared to the high-speed transmission of compact data over a dedicated channel.
It is desirable in many instances to dedicate an entire television channel to the transmission of data rather than video signals. Prior art systems for dedicated data channels typically require special transmitters and receivers different from those used for the transmission of video signals in order to achieve the desired high baud (bits per second) rate to efficiently utilize the channel bandwidth. This special data transmission equipment has resulted in substantial cost and complexity, particularly at each remote user terminal where a different receiver is usually required for each dedicated data channel. A simple and inexpensive system for the high speed transmission of data on a dedicated data channel has been greatly needed.